Modern parcel processing subsystems (e.g., FedEx, USPS, UPS, and the like) involve fairly large conveyors with high capacity and high throughput (e.g., four meters per second conveyor velocity).
Jams can occur on the conveyor between the side rails thereof, at corners or along curves, and/or where there are gaps in the side rails.
Prior photo-optic jam detection systems typically had an emitter on one side of the conveyor and a detector on the other side of the conveyor. With numerous adjacent articles on wide conveyors, false positive jam signals are the result.
U.S. Pat. Nos. 3,987,429; 4,258,250; and 8,630,537 are incorporated herein by this reference.